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  <div class="section" id="data-marshalling-support">
<span id="marshalling-utils"></span><h1>Data marshalling support<a class="headerlink" href="#data-marshalling-support" title="Permalink to this headline">¶</a></h1>
<p>These routines allow C code to work with serialized objects using the same
data format as the <a class="reference internal" href="../library/marshal.html#module-marshal" title="marshal: Convert Python objects to streams of bytes and back (with different constraints)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">marshal</span></code></a> module.  There are functions to write data
into the serialization format, and additional functions that can be used to
read the data back.  Files used to store marshalled data must be opened in
binary mode.</p>
<p>Numeric values are stored with the least significant byte first.</p>
<p>The module supports two versions of the data format: version 0 is the
historical version, version 1 shares interned strings in the file, and upon
unmarshalling.  Version 2 uses a binary format for floating point numbers.
<code class="docutils literal notranslate"><span class="pre">Py_MARSHAL_VERSION</span></code> indicates the current file format (currently 2).</p>
<dl class="function">
<dt id="c.PyMarshal_WriteLongToFile">
void <code class="sig-name descname">PyMarshal_WriteLongToFile</code><span class="sig-paren">(</span>long<em> value</em>, FILE<em> *file</em>, int<em> version</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_WriteLongToFile" title="Permalink to this definition">¶</a></dt>
<dd><p>Marshal a <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span></code> integer, <em>value</em>, to <em>file</em>.  This will only write
the least-significant 32 bits of <em>value</em>; regardless of the size of the
native <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span></code> type.  <em>version</em> indicates the file format.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyMarshal_WriteObjectToFile">
void <code class="sig-name descname">PyMarshal_WriteObjectToFile</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *value</em>, FILE<em> *file</em>, int<em> version</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_WriteObjectToFile" title="Permalink to this definition">¶</a></dt>
<dd><p>Marshal a Python object, <em>value</em>, to <em>file</em>.
<em>version</em> indicates the file format.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyMarshal_WriteObjectToString">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="sig-name descname">PyMarshal_WriteObjectToString</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *value</em>, int<em> version</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_WriteObjectToString" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a bytes object containing the marshalled representation of <em>value</em>.
<em>version</em> indicates the file format.</p>
</dd></dl>

<p>The following functions allow marshalled values to be read back in.</p>
<dl class="function">
<dt id="c.PyMarshal_ReadLongFromFile">
long <code class="sig-name descname">PyMarshal_ReadLongFromFile</code><span class="sig-paren">(</span>FILE<em> *file</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_ReadLongFromFile" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a C <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span></code> from the data stream in a <code class="xref c c-type docutils literal notranslate"><span class="pre">FILE*</span></code> opened
for reading.  Only a 32-bit value can be read in using this function,
regardless of the native size of <code class="xref c c-type docutils literal notranslate"><span class="pre">long</span></code>.</p>
<p>On error, sets the appropriate exception (<a class="reference internal" href="../library/exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>) and returns
<code class="docutils literal notranslate"><span class="pre">-1</span></code>.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyMarshal_ReadShortFromFile">
int <code class="sig-name descname">PyMarshal_ReadShortFromFile</code><span class="sig-paren">(</span>FILE<em> *file</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_ReadShortFromFile" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a C <code class="xref c c-type docutils literal notranslate"><span class="pre">short</span></code> from the data stream in a <code class="xref c c-type docutils literal notranslate"><span class="pre">FILE*</span></code> opened
for reading.  Only a 16-bit value can be read in using this function,
regardless of the native size of <code class="xref c c-type docutils literal notranslate"><span class="pre">short</span></code>.</p>
<p>On error, sets the appropriate exception (<a class="reference internal" href="../library/exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>) and returns
<code class="docutils literal notranslate"><span class="pre">-1</span></code>.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyMarshal_ReadObjectFromFile">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="sig-name descname">PyMarshal_ReadObjectFromFile</code><span class="sig-paren">(</span>FILE<em> *file</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_ReadObjectFromFile" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a Python object from the data stream in a <code class="xref c c-type docutils literal notranslate"><span class="pre">FILE*</span></code> opened for
reading.</p>
<p>On error, sets the appropriate exception (<a class="reference internal" href="../library/exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>, <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a>
or <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>) and returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyMarshal_ReadLastObjectFromFile">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="sig-name descname">PyMarshal_ReadLastObjectFromFile</code><span class="sig-paren">(</span>FILE<em> *file</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_ReadLastObjectFromFile" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a Python object from the data stream in a <code class="xref c c-type docutils literal notranslate"><span class="pre">FILE*</span></code> opened for
reading.  Unlike <a class="reference internal" href="#c.PyMarshal_ReadObjectFromFile" title="PyMarshal_ReadObjectFromFile"><code class="xref c c-func docutils literal notranslate"><span class="pre">PyMarshal_ReadObjectFromFile()</span></code></a>, this function
assumes that no further objects will be read from the file, allowing it to
aggressively load file data into memory so that the de-serialization can
operate from data in memory rather than reading a byte at a time from the
file.  Only use these variant if you are certain that you won’t be reading
anything else from the file.</p>
<p>On error, sets the appropriate exception (<a class="reference internal" href="../library/exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>, <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a>
or <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>) and returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
</dd></dl>

<dl class="function">
<dt id="c.PyMarshal_ReadObjectFromString">
<a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a>* <code class="sig-name descname">PyMarshal_ReadObjectFromString</code><span class="sig-paren">(</span>const char<em> *data</em>, Py_ssize_t<em> len</em><span class="sig-paren">)</span><a class="headerlink" href="#c.PyMarshal_ReadObjectFromString" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Return a Python object from the data stream in a byte buffer
containing <em>len</em> bytes pointed to by <em>data</em>.</p>
<p>On error, sets the appropriate exception (<a class="reference internal" href="../library/exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">EOFError</span></code></a>, <a class="reference internal" href="../library/exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a>
or <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">TypeError</span></code></a>) and returns <code class="docutils literal notranslate"><span class="pre">NULL</span></code>.</p>
</dd></dl>

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